There are several types of prior art dispensing systems used for dispensing metered amounts of liquid or paste for a variety of applications. One such application is in the assembly of printed circuit boards and integrated circuit chips. In this, application, dispensing systems are used in the process of encapsulating integrated circuits with an encapsulating material and in the process of underfilling flip integrated circuit chips with an encapsulant. Prior art dispensing systems are also used for dispensing dots or balls of liquid epoxy or solder paste onto circuit boards and integrated circuits. The liquid epoxy and solder is used to connect components to a circuit board or to an integrated circuit. The dispensing systems described above include those manufactured and distributed by Speedline Technologies, Inc., assignee of the present invention, under the name CAMALOT™.
The dispensing systems described above are typically used in an electronics manufacturing facility in an automated assembly line with other equipment used in a circuit board or integrated circuit manufacturing process. The other equipment in-line with the dispensing systems may include, for example, pick and place machines, which place components on circuit boards, or reflow ovens that are used to cure materials dispensed onto the circuit boards or integrated circuits.
In a typical dispensing system, a pump and dispenser assembly is mounted to a moving assembly for moving the pump and dispenser assembly along three mutually orthogonal axes (x, y, z) using servomotors controlled by a computer system or controller. To dispense a dot of liquid on a circuit board at a desired location, the pump and dispenser assembly is moved along the horizontal x and y axes until it is located over the desired location. The pump and dispenser assembly is then lowered along the vertical z axis until the nozzle of the pump and dispenser assembly is at an appropriate dispensing height over the board. The pump and dispenser assembly dispenses a dot of liquid, is then raised along the z axis, moved along the x and y axes to a new location, and is lowered along the z axis to dispense the next liquid dot.
During the manufacture of circuit boards, a conveyor system is typically employed to transport the circuit boards through several processing stations associated with the dispensing system. It is sometimes necessary, or desirable, to process differently sized circuit boards. As a result, spacing between conveyor rails of the conveyor system requires adjustment. Typically, an operator of the dispensing system is required to physically move the conveyor rails to adjust the spacing of the rails to accommodate the differently sized circuit board. In this arrangement, the operator is required to re-adjust the spacing of the conveyor rails each time a differently sized circuit board is transported on the conveyor rails of the conveyor system.
One deficiency with requiring an operator to re-adjust the conveyor rails of the conveyor system, as described above, relates to reduced output of the circuit board manufacturing process. In particular, the circuit board manufacturing process needs to be stopped for a period of time to enable the operator to re-adjust the spacing of the conveyor rails. Stopping the circuit board manufacturing process for a period of time significantly reduces volume production and adds significant costs to the final products produced. Another deficiency of this re-adjustment requirement is related to operator error. If the operator fails to precisely space the rails of the conveyor system, the circuit boards can either fall off of the conveyor system (e.g. rails spaced to far apart) or the circuit boards can become jammed in other machinery associated with the conveyor system (e.g. rails spaced to close together).
Some conveyor systems include motorized rails for reducing operator intervention during the process of re-adjusting rails of the conveyor system. In this type of conveyor system, for example, a motor is coupled to at least a first rail of the conveyor system. The motor is used to move the first rail relative to an adjacently positioned second rail to adjust a space between the first rail and the second rail to accommodate different size circuit boards. In operation of this conveyor system, the motor is initially controlled to move the first rail to a reference position. The motor is thereafter controlled to move the first rail from the reference position to a position for carrying the circuit boards, which is a predetermined distance from the reference position. The predetermined distance for which the first rail is moved is typically measured by an encoder that is coupled to the motor.
One deficiency with this type of conveyor system relates to the time required to initialize the position of the first rail during system start-up, after a power loss or after a system reset. Other deficiencies with this type of conveyor system can occur if the conveyor system includes multiple conveyor lanes. The multiple lane conveyor system can include a plurality of pairs of rails, for which some or all of the rails may require initial positioning at the reference position, as previously described. Further, during the course of operations using the multiple lane conveyor system it may become necessary to re-adjust fewer than all of the lane widths, which would require fewer than all of the motorized rails to return to the reference position and then move to an operating position.
One deficiency occurs in that adjacent lanes that do not require lane re-adjustment may be positioned intermediate the lane that requires re-adjustment and the reference position, thus blocking the motorized rail from moving to the reference position without disturbing the operating position of the adjacent lanes that do not require lane re-adjustment.
Therefore, a need exists for a control system and method for controlling a conveyor system to precisely adjust conveyor rails of the conveyor system to accommodate differently sized substrates, which overcomes the deficiencies and limitations described above.